The present invention relates to gas fueled ovens and particularly to a built-in double wall oven having pyrolytic self-cleaning capability.
The outer surfaces of built-in wall ovens contact or are in close proximity with adjacent and supporting structures which often are fabricated of wood. Accordingly, the temperature of the outer surfaces of a built-in wall oven must be maintained below a level that would cause damage to the household or even start a fire. With conventional built-in wall ovens that do not have the self-clean feature, sufficient insulation has been an acceptable solution to limiting external surface temperatures because the oven compartment typically does not exceed 500.degree.-550.degree. F. However, with a self-clean oven, the oven compartment is heated in the range from 900.degree.-1100.degree. F. for several hours during a pyrolytic cycle. The use of insulation alone is not generally practical for a built-in wall oven under these extreme conditions of temperature and time. Because of the very high temperatures, a significant amount of heat passes through any practical type and thickness of insulation, and, with the confinement of a built-in wall oven, extremely hot and perhaps damaging external surface temperatures could be reached.
Such as described in U.S. Pat. No. 4,375,213, attempts have been made to overcome the above-described problem by encasing a built-in wall oven with a spaced jacket or outer casing that defines an air chamber surrounding the oven compartment. A fan was used to force air through the chamber so as to remove substantial amounts of heat which pass through the insulation layer. In this way, the temperature of the jacket or casing is controlled to an acceptable level.
Because built-in wall ovens are generally encased on all sides except for the front, the above-described cooling air must be drawn in and expelled from the front surface. With an electric oven, this generally is no problem because there is sufficient surface area on the front to accommodate apertures for drawing in and expelling the cooling air. However, with a gas oven, there are other requirements for the limited surface area on the front. More specifically, with a gas oven, both primary and secondary combustion air and the combustion products must pass through vents on the front, and as recognized in U.S. Pat. No. 4,375,213, the cooling air should be isolated from the combustion air so as to provide proper burning characteristics. Because it is desirable to limit the front surface area of a built-in wall oven, there are tight constraints for the entrance and exhaust of cooling and combustion air from a gas wall oven. This problem is made more severe with a double wall oven because combustion products are exhausted from two oven cavities.